Process for improving the properties of regenerated cellulose fibrous material wherein said material is treated while still in the gel state



Sept. 1, 1959 I G. c. DAUL ETAL 2,902,391

PROCESS FOR IMPROVING THE PROPERTIES OF REGENERATED cELLuLosE FIBROUS MATERIAL WHEREIN SAID MATERIAL Is TREATED WHILE STILL IN THE GEL sTATE Filed Jan. 23, 1957 OPENER G) com/v0 34 p/m/vo 13 REGENERAT/O/Y aesuLnm/zAr/aw Jdl/Rl/VG c 0772mm mvenfors George C. 000/ Q Ham/d F W/se By f/Ie/r af/omeys Ja/m Who/Ian I United States Patent() RIAL WHEREIN SAID MATERIAL Is TREATED WHILE STILL IN TH GEL STATE George Daul, Mobile, Harold F. Wise, Spring Hill,

and John Wharton, Mobile, Ala, assignors to Courtaulds Inc., New .York, N .Y., a corporation of Delaware Application January 2 3, 1957, Serial No. 635,695

*11 Claims. (CL 117-145 This invention relates to a process for improving the properties of regenerated cellulose fibrous material and in particular to a process for introducing heat hardenable resinous materials into regenerated cellulose fiber.

Many attempts have been made to treat cellulosic materials with synthetic resins of various types such, for example, as the aminoplasts and, more recently, polyepoxy compounds. In general, resin treatment of regenerated cellulose fibrous materials is carried out on cloth to obtain crease resistance and dimensional stability. However, up until the present time it has been difiicult with such treatments to get thorough, uniform penetration of the fibers without leaving an excessof resin on the surfaces of the fibers. When it is attempted to treat staple fibers, the problem becomes particularly acute. Staple fibers are normally. processed in the form of a mat or blanket, and in. this case, treatment with a resin forming material followed by drying and curing has led to stuck fibers and lumps of fibers which are extremely difiicult and often impossible to process into yarn and cloth.

It has been attempted to overcome this difficulty by subjecting staple fibers, following treatment with a solution of resin forming materials, to centrifuging at high speeds. This further treatmcnL however, is only partially successful in removing excess resin andis, in'any case, time consuming and impractical from a continuous production standpoint. i

It is an object of the present inventionto provide a new, convenient and economical way for treating regenerated cellulose fibers with heat hardenable resin forming solutions.

It is further an object of the invention to provide a method which is simple and economical and by which a reisnous solution or dispersion may be introduced into the interior of the fibers to be treated.

It is a further object of the invention to provide a method; for treatment of regenerated cellulose fibers with resin forming solutions in which deposition of excess resin on the outside of the fibers is avoided.

It is a further object of-the invention to provide a simple and economical process whereby regenerated cellulose fibrous material having improved properties may be produced. I

In accordance with the invention, .these and other objects are attained by a method which comprises treating cellulosic fiber while it is still in the gel state and before it has been dried sufficiently to convert it from the gel state, with an aqueous liquid containing a heathardenable resinous material, and then reducing the liquid content of the fiberto below the normal water imbibition of the fiber in the gel state. Preferably reduction of the liquid content is eifected by squeezing.

The present invention is based on the discovery that the optimum time'for treatment of regenerated cellulose fibrous material with a resinous liquid is before any drying of the fiber has taken place and while the fiber is still in the initial gel or swollen state after its formation. It hasqbeen discovered that in this initial gel or swollen state, fibers have their highest degree of absorptive power, much higher than at any other time in their existence. Furthermore, it has now been found that by reducing the liquid content of the fibers to below their normal waterimbibition value in the gel state, there is in effectcreated a kind of negative pressure inside the fibersmIf the fibers have been previously immersed in or contacted with a resinous solution or dispersion, they draw the resin-containing liquid remaining on the fibers after squeezing into the interior of the fibers ratherthan permitting it to remain and accumulate outside. I I I p I The absorptive power of regenerated cellulose fiber is measured 'by what is known in the industry as the water imbibition value which is defined as the percent by weight of water retained insaturated material after centrifuging an 0.5 gm. sample for five minutes at 1,000 G anduis expressed as percent of the oven-dry weight of: thefiber (see Journal of the Society of Dyers and Colorists, October 1948, page 331). Y I

The water imbibition values for once dried normal textile rayon fibers are in the range of. 90% to 115%. When fabricsmade from such fibers are treated in the usual fashiornwith :resin precondensates for efifects such as crease resistanceand dimensional stability, even with the high mangle pressures used; in conventional equipment, liquidretention,.of. the padded fabric is in this approximate range... On the other hand, the water imbibition values .of. never-dried normal textile rayon fibers are in the rangeof 120% to 150%. It has been found, surprisingly, thatby squeezing never-dried rayon fiber whilestill in the gel state it. is possible to reduce the moisture content of this material much .below the water imbibitiomrange cited. Thus, fibers having a gal water imbibition value of 145%. may be squeezed to. contain as little; as 60% moisture on the oven-dry weight of the fiber. When this is done. after the fiber is brought into contact with a. resin precondensate solution, it acts like a sponge which has, newly been squeezed out and draws in, the excess resinous precondensataleaving little.

to remaiiron the surface. of the fibers. I

The invention is applicable to regenerated cellulose made by any of. the conventional techniques, i.e.. by the viscose, cuprammonium on nitrate processes. However, it is preferred touse regenerated cellulose which has been made ,by the viscose process.

By certain variations in coagulating and spinning techniques, well-knownto the art, it is possible to obtain.

viscose rayon having. never dried imbibition values from 60% to say 150%. The lower the water imbibitiornthe more pressure must be exerted tosqueeze the,

fiber to a liquid contentbelow the water imbibition value. For'this reason, while the invention is applicable to fibersfof Lall water imbibition values, best results are obtained from fibers having high gel water imbibition values'and especially those having gel water imbibition values or to a The invention is applicable to all forms offibrous regenerated cellulose, to both staple and. continuous filamentfibers. Howeverjit is of particular importance in,

the treatmentof staple fiber.

The heat, hardenable resinous materials which applied by means of the present invention are those custornarily used in the textile ]industry. :These inelnde amjnoplasts, which may be defined as heathardenable resins which are the condensation products ofeompounde;

having at least two amino hydrogens,withmethylol form ing compounds; 'Ifypicalarninoplasts are urea-forrnalde;

hyd, mlamine formaldehyde, dicyandiarnideformaldef hyde, guanidine-formaldehyde and combinationsof these ingredients. The term is also used to include the methylol-amino-epihalohydrin compounds described in the copending application of George C. Daul, Serial No. 563,- 429, filed February 26, 1956.

Other resinous materials which are suitable for use in the present invention are those formed by the reaction of formaldehyde and acrolein as described in United States Patent No. 2,696,477; resins formed by the reaction of acetone and formaldehyde as described, for example, in United States Patents No. 2,504,835 and No. 2,711,971; and polyepoxy resins, e.g. polyfunctional compounds having at least two epoxy group-s linked through a hydrocarbon, a polyhydric phenol or a polyhydric alcohol group, such as the resins formed from saturated polyglycidyl ethers of polyhydric alcohols as described in United States Patent No. 2,752,269. Particularly useful compounds of the last named class are the condensation products of epichlorohydrin with ethylene glycols. It will be understood that the precise resin used is not a part of the present invention and other heat hardenable resins used in the textile industry may be employed as desired.

Preferably the resinous materials are applied while they are in a state such that they will form aqueous solutions or stable dispersions containing at least 3% resinous material, and such that the average molecular size of the material is sufliciently small to enable the resin molecules to penetrate into the fiber in the gel or never dried state. In general these conditions will be met by applying the resinous material while it is in substantially precondensed, monomeric or low polymer state, and while the molecular weight is on the order of 1001000, preferably not exceeding about 600, it being recognized that the extent of polymerization which is permissible Will depend on the type of resin being employed. The average particle size should in any case be below 0.1 micron. Normally, freshly prepared precondensates are preferable to aged material.

The resinous material or precondensate is preferably applied as an aqueous solution or stable dispersion. The resin concentration in the impregnating solution or dispersion will vary with the particular resin and with the type of fiber treated. Usually it Will be between about 3% and about 20% by weight of the solution. The impregnating liquid may also contain various ingredients other than the resin precondensate or its components. For example, it may contain from 2% to 20% on the weight of the resin of a catalyst to aid in curing the precondensate. Obviously the type of catalyst used will depend on the particular resin used. The liquid may also contain from 0.1% to 4% on the weight of the liquid of a finishing agent. The finishing agent may be selected to add lubricity, cohesion, water repellancy, scroop or other desired properties to the fiber. Materials well-known to the art, such as polyglycol stearate, lauryl ketene dimer, silicone emulsions, stearamido methyl pyridinium chloride, octadecyl pyridinium sulfate and others may be used alone or in combination for this purpose.

The temperature of the resin impregnating solution is not a critical factor and will vary with the particular resin being applied. Normally, it will be between about and about 50 C., preferably between about and about 40 C.

The manipulative steps which are used in carrying out the invention depend to a certain extent upon the form of the fibrous material which is being treated. Thus, a different mechanical technique would be used in applying a resin solution for a continuous filament than would be used in treating staple fiber. Staple fiber is in general treated in the form of a mat or blanket in which the fiber is arranged more or less at random. The thickness of the blanket is, in general, not a critical factor and the process may be employed with blankets of various thickness, although normally the blanket thickness will 4 be between about one-half inch and about two and onehalf inches.

The technique used in carrying out this invention is to pass the blanket between squeeze rollers to remove a large portion of the final wash water, then bring it into contact with the resin-containing liquid which is usually applied as a heavy spray onto the blanket. When the blanket has been wet thoroughly with the resinous liquid, it is moved between another pair of rollers where it is squeezed to remove excess liquid. This process may be repeated several times to obtain uniform resin distribution and increase the total solids pickup. While there is no limit on the number of times the contacting step may be repeated, it has been found that four resin baths are usually suflicient.

The blanket, thoroughly wet with the resinous liquid then passes through squeeze rollers adjusted to remove enough liquid from the blanket so that the remaining liquid content is less than the normal water imbibition value of the fiber (in the gel state). In most cases, when the invention is applied to textile grade fiber, the liquid content is reduced to 10 to 65% below the gel water imbibition value which is equivalent to a liquid content'of 60% to 120% on the weight of the oven-dry impregnated fiber. The pressure required to accomplish this will vary with the past history of the fiber and with the thickness of the blanket, but will, in general, be between about 500 and about 3500 pounds per linear inch of A convenient way to determine the liquid content is to weigh the fiber immediately after squeezing and then dry it in the manner outlined below. During drying, water and a certain amount of formaldehyde may be driven off. The dried fiber is Weighed and the difierence in the two weights taken. The liquid content of the squeezed fiber, for purposes of the present invention, may then be calculated as After passing through the final squeeze rollers, the blanket may be opened by conventional methods, spread on a moving conveyor belt, dried and cured. The temperatures and conditions of drying and curing will depend on the particular resin being employed. However, in general the impregnated fiber will be dried between about 50 and about 100 C. for whatever time is required to bring the moisture content of the fiber into equilibrium with its environment. Normally this will be between about about 10 and about 4 5 minutes.

Curing is usually conducted at a temperature of between about and about C. for between about 3 and about 30 minutes. The precise time and temperature will vary with the particular resin being used.

The invention will be further described in connection with the accompanying figure which is a schematic flow diagram illustrating treatment of viscose staple fiber in accordance with the invention.

Referring to the figure, a regenerated cellulose tow 10 is formed in conventional fashion by extruding viscose from a spinnerette 11 into a coagulating bath 12. The bath 12 may be of any conventional composition comprising for example, between about 7% and about 12% H 80 between about 14% and about 25% Na SO from 0 to about 8% ZnSO and from 0 to about 10% MgSO Other ingredients well-known to the art such, for example, as surface-active agents for preventing spinnerette incrusta-tion, may also be present. The temperature of the bath will normally be from say 40 to 60 C.

The tow is Withdrawn from the coagulating bath 12 and, in accordance with conventional practice, is cut up into staple fiber by a cutting device 13. The staple falls on a continuous belt 14 and forms a mat or blanket 15 thereon, It may then be subjected to conventional regenerating, washing, desulfurizing and like treatments. Thus, for example, it may be subjected to an aqueous spray 16 containing from 1% to 2% H 80 at a temperature of from 60 to 92 C. Following this, is may be given a neutral or slightly alkaline wash 17 (pH 7.5-9.5) at a temperature of say 75-90 C.

Following the neutralizing wash 17, the blanket may be treated with a desulfu-rization wash 18 containing from say 0.1% to 0.4% Na s at a temperature of between about 55 and about 70 C. This wash may also contain up to about .4% of sodium carbonate or sodium hydroxide together with sequestering or wetting agents if desired.

The desulfurization treatment is then normally followed with a sulfide wash 19 comprising neutral water at 7090 C. to remove sulfide liquors. In accordance with usual practice, a sour or acid wash 20, containing between about 0.2% and about 0.5% H SO 1orHCl at a temperature of 2025 C. is then employed. An additional water wash 2.1 at a temperature of say 60-85 C. follows to remove acid. The blanket is then squeezed to remove excess water by passing it between squeeze rolls 22 and 23.

i In accordance with the invention the squeezed gel fiber is now passed over another endless belt 24 where it is subjected to an aqueous liquid 25 containing between about 3% and about by weight of a heat hardenable resinous material, at a temperature of between about 20 C. and about 40 C. The liquid may also contain a catalyst, the amount of catalyst being in general from about 2% to about 20% on the weight of the resinous material, the exact amount depending upon the concentration and kind of resin used. The liquid may further com prise from say 0.1% to 4% of a finishing agent of any of the types customarily used in the art.

If desired, the blanket can be taken directly from treatment at 25, squeezed until its liquid content is below the gel water irnbibition value and passed to a curing and drying stage. However, in the embodiment of the invention shown in the figure there is an additional resin impregnation step. Thus the blanket, having been treated at 25, is again subjected to a squeezing between rollers 26 and 27, then delivered to another endless belt 35 where it is contacted with additional resin solution at 28, the resin solution at 28 being preferably the same as that at 25. Further resin treatments may be added, as desired, although these are not shown in the figure.

After the final resin treatment the blanket is passed through final squeeze rolls 29 and 30 where it is squeezed with sufficient pressure to reduce the amount of liquid in the fibers to below the water imbibition value of the gel fiber. When the blanket leaves this set of squeeze rolls, substantially all of the resin-containing liquid is drawn into the fibers leaving only the larger molecular size finishing agents on the surfaces of the fibers. The total of resin-containing liquid in the treated fiber is now between about 60% and 120% on the weight of the oven-dry treated fiber. The blanket is then delivered to a conventional opening device 31 where the blanket is pulled apart. The resulting fibers are delivered to another endless belt 32 which carries themthrough to a drying oven 33 where they are dried at a temperature which is normally between about 200 and about 240 F. The dried fibers are then passed through a curing oven 34 where they are cured at a temperature of say 260 to 350 F.

The fibers obtained from the process have low water imbibition. They may be processed without difficulty on conventional cotton spinning machinery without the danger of excessive fly or breaking of the fibers. The material has a good hand and is altogether satisfactory for all textile purposes.

The invention will be further described in reference to the following specific examples. It is understood that these examples are given for purposes of illustration only and are in no way intended as restricting the invention beyond the scope of the appended claims.

Example I A blanket of freshly spun never-dried viscose rayon fiber (textile grade) still in the gel state after spinning and having a water imbibition' value of 145% was squeezed between pressure rolls to a liquid retention of on the weight of the oven-dried cellulose. The blanket was two inches thick and the pressure of the rolls was 850 pounds per lineal inch of nip. The squeezed blanket was then passed under a spray of an aqueous solution containing 9% of a urea-melamine-epichlorohydrin: formaldehyde precondensate of the type described in the copending application of G. C. Daul, Serial No. 563,429, filed February 26, 1956. The ratio of urea to melamine to epichlorohydrin to formaldehyde in this precondensate was 1:112:45. The solution also contained 0.75% magnesiurn chloride hexahydrate catalyst, and 0.15% of a polyglycol stearate softening agent.

The impregnation was carried out in two steps with an intermediate squeeze and a final heavy squeeze between pressurized rolls (850 pounds pressure per lineal inch of nip) to a final liquid retention of 100% on the oven-dry weight of the treated cellulose. The fiber blanket was then opened, dried at a temperature of 210 F., and cured at a temperature of 320 F. The water imbibition value of the product was 40%. Its dry tenacity was the same as for an untreated sample; its wet tenacity was increased 50% over that of an untreated sample and its elongation was reduced 48%. The fiber was processed on a picker, card, drawing frame and spinning machine. It was then made into cloth without difliculty.

The above experiment was repeated with the difierence that the pressurized squeeze rolls after resin liquid contact was gauged to give a liquid retention by the fiber blanket of (the same as the water imbibition of the never-dried fiber). The finished product, while it could be processed with difiiculty, exhibited excessive fly on the carding machine. There were many stuck fibers and uneven yarn resulted.

The experiment was again repeated using a pressure to give a liquid retention by the blanket of (15% in excess of the water imbibition value of the never-dried fiber) after contact with resin. The finished product was matted, fibers were stuck together with resin and it could not be processed.

Example [I The procedure of Example I was followed to treat textile grade rayon fiber still in the gel state with a liquid bath containing 5% by weight of an acrolein-formaldehyde precondensate (1 mol acrolein: 4 mols formaldehyde), 5% of a urea formaldehyde precondensate (1 mol urea: 1.6 mol formaldehyde), 0.75% magnesium chloride hexahydrate (catalyst) and 0.15% ofa lauryl ketene dimer and 0.15% polyglycol stearate (finishing agents). The impregnated fiber blanket was then squeezed sufficiently to reduce the liquid content to 90% of the weight of the cellulose. The blanket was then opened, driedand cured as before.

The treated fiber had a water imbibition value of 44% and was readily processable on conventional textile machinery.

Example III The procedure of Example II was used wherein the treating bath contained 15% of an acetone-formaldehyde precondensate (1 mol acetone: 4 mol formaldehyde), 4% sodium carbonate (catalyst), and 0.15% lauryl ketene dimer, 0.15% polyglycol stearate (finishing agents). A product having properties similar to that obtained in Example II resulted.

Example IV The procedure of Example II was used wherein the treating bath contained 12% of a polyepoxy-polyglycol 7 precondensate (Eponite 100), 1.5% zinc fiuoboralte (catalyst), 0.6% polyvinyl alcohol (emulsifier) and 0.15% epoxidized soyabean oil (finishing agent). In this case the fiber blanket was squeezed to retain 85% of the weight of the liquid on the cellulose, or 60 percentage points below the gel water imbibition of the fiber (145%). Similar results were obtained.

Example V The procedure of Example I was repeated using viscose rayon having different water imbibition values and precondensate baths of different concentrations. The results are listed in the table below:

Water Coneen- Liquid Processing Report Imbibition tration retained Rayon value of of preby fiber type never-dried condensate after Draw rayon, used final Gard frame Spinning percent squeeze, percent 80 6.0 60 good. good good. 80 6.0 75 good fair. fair. 80 6.0 80 fair poor poor. 80 6.0 90 bad"- bad.. bad. 110 7.5 70 good good good. 110 7.5 95 good good good. 110 7.5 110 poor fain--. poor. 110 7.5 115 bad... bad would not spin. 144 8.0 90 good good good. 144 8.0 120 goo good.. good. 144 8.0 144 fair poor poor. 144 8.0 150 bad bad. Wouldnot In the above examples it may be seen that in all cases where the final squeezing of the precondensate-impregnated rayon was sufiicient to reduce the amount of liquid in the rayon to below the water imbibition value of the never-dried fiber used, acceptable processability resulted.

Whenever the amount of precondensate retained by the fiber was equal to or above the never-dried water imbibition value of the rayon used, processing became increasingly difficult with an increase 'in the amount of liquid retained.

Although the invention has been particularly described with reference to the treatment of staple fiber, it can obviously be applied as well to continuous filament or other types of fiber. Details of the mechanical handling of the fibrous material may vary in such cases. For example, resin contact of continuous filament fiber may be carried out while the filament is wound on a reel or spindle, in the form of a cake or cheese, or by passage of the filament through a bath.

Similarly, although it is preferred to reduce the water content of the fibrous material by means of squeeze rollers, a similar effect can be obtained by dehumidifying the material by other means, for example, by vacuum squeeze rolls in which liquid is sucked from the nip of the rolls by vacuum. In using such other means, however, care must be taken that the fiber is not converted from the gel state.

We claim:

1. A method for impregnating regenerated cellulose fibrous material with a heat hardenable resinous material which comprises treating the fibrous material while it is still in the gel state, and before it has ever been dried sufficiently to convert it from the gel state, with an aqueous liquid containing a heat hardenable resinous material having a molecular Weight between 100 and 1000 and then mechanically reducing the liquid content of the treated fiber to less than the normal water imbibition value of the fiber in the gel state.

2. The method claimed in claim 1 wherein the cellulose fib'rous material is staple fiber.

3. The method claimed in claim 1 wherein the heat hardena'ble resinous material is selected from the group consisting of aminoplast, acrolein-fornialdehyde, acetoneformaldehyde and vpolyepoxy resinous materials.

4. The method claimed in claim 1 wherein the aqueous liquid contains between about 3 and about 20% by weight of the resinous material.

5. The method claimed in claim 1 and comprising subsequently drying the fibrous material and curing the resin in the dried material.

6. The method claimed in claim 1 and comprising contacting the fibrous material with the resinous material in a plurality of stages.

7. A method for impregnating regenerated cellulose staple fiber with a heat hardenable resinous material which comprises treating said fiber with an aqueous liquid containing a precondensate of said resinous material having a molecular weight on the order of to 1000 while said fiber is still in the gel state and before it has ever been dried suificiently to convert it from the gel state, and then squeezing the impregnated fiber until its liquid content is less than the normal water irnbibition of the fiber in the gel state.

8. The method claimed in claim- 7 wherein the heat hardenable resinous material is selected from the group consisting of aminoplast, acrolein-formaldehyde, acetoneformaldehyde and polyepoxy resinous materials.

9. The method claimed in claim 7 wherein the fiber is dried and heated to cure said resinous material.

10. A method for impregnating regenerated cellulose fibrous material having a gel water imbibition of between about and with a heat hardenable resinous material which comprises treating said fibrous material while it is in the gel state and before it has ever been dried sufficiently to convert it from the gel state with an aqueous liquid containing a precondensate of said heat handenable resinous material having a molecular weight on the order of 100 to 1000 and then squeezing the treated fibrous material until its liquid content is between about 60% and about 120% by weight of the oven dried treated fiber, drying said squeezed fibrous material and curing the dried material.

11. A method for impregnating regenerated cellulose staple fiber with heat hardenable resinous material which comprises treating said fiber with an aqueous liquid containing a precondensate of said resinous material having a molecular Weight on the order of 100 to 1000 while said fiber is still in the gel state and before it has. ever been dried, mechanically reducing the liquid content of the impregnated fiber until its liquid content is less than the normal Water imbibition of the fiber in the gel state, and then drying the impregnated fibrous material containing the reduced amount of liquid.

References Cited in the file of this patent UNITED STATES PATENTS 2,394,009 Pollard Feb. 5, 1946 2,575,443 Cornwell Nov. 20, 1951 2,709,146 Berry et al May 24, 1955 

1. A METHOD FOR IMPREGNATING REGENERATED CELLULOSE FIBROUS MATERIAL WITH A HEAT HARDENABLE RESINOUS MATERIAL WHICH COMPRISES TREATING THE FIBROUS MATERIAL WHILE IT IS STILL IN THE GEL STATE, AND BEFORE IT HAS EVER BEEN DRIED SUFFICIENTLY TO CONVERT IT FROM THE GEL STATE, WITH AN AQUEOUS LIQUID CONTAINING A HEAT HARDENABLE RESINOUS MATERIAL HAVING A MOLECULAR WEIGHT BETWEEN 100 AND 1000 AND THEN MECHANICALLY REDUCING THE LIQUID CONTENT OF THE TREATED FIBER TO LESS THAN THE NORMAL WATER IMBIBITION VALUE OF THE FIBER IN THE GEL STATE. 